msm: pil-venus: Use mem_setup hook to get fw_size

fw_size is calculated from the device tree properties. Now that
we have a mem_setup hook, use that to program the size of the
firmware into the hardware. Remove the out of bounds check in
init_image() too because the PIL core handles that now.

Change-Id: I4b415ab5b97e84586c495a767b3a2bb47520e135
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>